Accumulation of Al, Mn, Fe, Cu, Zn, Cd and Pb by the bryophyte Scapania undulata in three upland waters of different pH

Measurements were made of the contents of Al, Mn, Fe, Cu, Zn, Cd and Pb in Scapania undulata in three streams (D2, D5, D11) in the English Lake Distri ct. The stream waters had average pH values of 5.35 (D2), 5.81 (D5) and 7.2 6 (D11), the main differences in other major chemical components being in M g, Al, Ca and alkalinity. There was generally more metal accumulation in th e older parts of the plants, but this was not significant in ail cases. Ext ents of accumulation varied with stream pH and dissolved metal concentratio n. For Al, accumulation was greatest in streams D2 and D5. Mn accumulated m ost in D5 and Fe was without preference. Cu, Zn and Cd accumulated mostly i n the plants in stream D11 and Pb accumulated more in D5 and D11. In terms of enrichment factors (amount of metal in the plants divided by stream wate r concentration) the sequence was Zn < Cd < Cu < Mn < Pb < Al < Fe. Laborat ory experiments supported the findings of the field data, providing evidenc e that uptake increases with pH at constant total metal concentration. The results are interpreted qualitatively in terms of the chemical speciation o f the metals in the stream water and competition between metal ions and pro tons at the plant-water interface. It is suggested that Al, Cu, Zn, Cd and Pb behave according to chemical complexation, whereas redox processes and/o r colloidal interactions may be significant for Mn and Fe. (C) 2001 Elsevie r Science Ltd. All rights reserved.